This invention relates generally to friction discs intended for use in clutches, such as for example motor vehicle clutches, and it relates more particularly to those friction discs comprising a central boss or flange and a plurality of radial blades integral therewith each fitted with an individual friction lining on each outer face, the said blades each being formed by two plates which, at least over their operative portion, i.e. the portion having the friction lining, are spaced from each other, with the intervention of resilient means applying an axial thrust which urges the plates apart from each other, these plates being attached to each other by coupling means with a unidirectional axial action adapted to limit the spacing of the plates.
As a result of the resilient means provided within these blades, a friction disc of this kind has axial resiliency which is favourable to the satisfactory engagement of the clutch with which it is associated, and favourable to reduced wear of the friction linings; when the clutch is disengaged, the plates which constitute the blades of its friction disc are at an axial spacing from each other and, when the clutch is engaged, i.e. when it is moved into the engaged position, the pressure elements which establish this engagement first of all cause the plates to move together in the axial direction, to meet the resilient means inserted between the plates, before effecting positive locking of the blades as a whole.
A friction disc of this kind with axial resiliency is described in U.S. Pat. No. 3,526,307.
The teaching of this U.S. patent, which is the most commonly used solution, is that the coupling means with a unidirectional axial action which connect each pair of plates consist of small columns or lugs formed separately from the plates and attached to one of them e.g. by crimping, the said lugs passing, with some play, through passages formed for this purpose in the other plate, and comprising, beyond the plates, a shoulder adapted to co-operate with the latter plate by abutting thereon.
This construction has a number of disadvantages.
Firstly, since it uses special parts which have to be made individually and then assembled with the plates, it is relatively expensive.
Moreover, the lugs used result in practice in the presence of a not inconsiderable axial projection on each of the faces of the blades of the friction disc, and because of the corresponding circumferential dimensions, this inevitably limits the surface area of these blades over which the friction linings can extend.
Consequently, for a particular surface area of the blades, there is a limitation, possibly a detrimental limitation, of the surface area of the friction linings carried on the blades, or, for a given surface area of the friction linings, there is an increase in the surface area required for the blades, which is always expensive since it involves a larger amount of material.
In British Pat. No. 1,170,215, the coupling means with a unidirectional axial action which connect each pair of plates are integral with these plates, thus avoiding at least some of the disadvantages mentioned above.
However, in the construction proposed in this British Pat. No. 1,170,215, these coupling means act fully on the surface, i.e. at a spacing from the contours of the plates in question, and these coupling means comprise a lug formed in one plate and engaging in an opening formed in the other.
This makes assembly of the disc more complicated.
It also means that each blade has to be formed by two separate parts, thus increasing the price of the assembly.
The present invention relates generally to a construction of the coupling means with a unidirectional axial action which is both simple and economical to achieve in practice.